To work out resistances in series:
RT = R1 + R2 + .......
To work out resistances in parallel:
RT =
when there are more than 2 in parallel:
1

RT
Q1/
R1 x R2

R1 + R2
1
1
1
 +  + 
R1
R2
R3 .......
=
The following light bulbs have a
resistance of 10Ω. When they are
wired together in series what is the total
resistance RTOTAL ?
RTOTAL
If the bulbs are now wired in parallel,
what will be the value of RTOTAL ?
Q2/
Q3/
In the diagram is a circuit to
connect a speaker to an
amplifier.
The amplifier must have a load
resistance of 64Ω, but the
speaker is only 8Ω.
What value must the resistor R
be to produce a total of 64Ω ?
A meter needs to have a
30Ω resistor in series with it.
The nearest preferred value
is 33Ω.
What value must resistor R
equal when in parallel with
the other, to produce a total
resistance of 30Ω ?
or
RTOTAL
R
From
amplifier
Total resistance
must equal 64Ω
Speaker
8Ω
33 Ω
30 Ω
Test
probes
R
Meter
240Ω
Q4/
Try and work out the total
resistance of this network between
A & B? (Tip: Pair similar values)
40Ω
A
240Ω
B
80Ω
120Ω
PTD - 96
40Ω
Answers
Q1/
a) 20 ohms
b) 5 ohms
Q2/
56 ohms
Q3/
330ohms
Q4/
100 ohms